Generally speaking metals may be obtained from their ores by processes starting with compounds such as oxides or halides of the desired metal, which are reduced chemically or electrolytically. Very electropositive metals whose compounds are therefore difficult to reduce are often treated chemically by low-cost products such as hydrogen, carbon, or carbon monoxide at a very high temperature which causes the formation of stable carbides which make it impossible to prepare sufficiently pure metals. It is therefore necessary to use chemical reducing agents which are much more expensive such as alkali metals or alkaline earths, magnesium or silicon, or to employ electrolytic reduction which uses large quantities of electricity.
The alloys of these metals are usually obtained by simultaneous fusion of the elements of the alloy when their melting points are substantially equal. When this is not the case, the less easily melted metals are dissolved in the other previously molten metals. This latter operation is usually unduly long with certain refractory metals and requires an atmosphere which is preferably inert at the elevated temperatures required to obtain sufficiently rapid dissolution. It is also very difficult to react at high temperature a relatively volatile metal with a refractory metal and problems with contamination from the containing vessel arise.
The processes as well as the suspension furnaces which are used to prevent the alloy from reacting with the receptacle are very difficult to use and extremely expensive. In addition they are only nominally useful for large-scale industrial production of alloys. Finally this preparation of alloys by direct action of the elements requires that the individual elements themselves be prepared as powders, for the refractory metals in a high degree of purity and, in certain cases, be absolutely pure, which is once again difficult to achieve and expensive.